Not a day goes by without us getting smaller. So far from the medieval picture of us as the centre of the heavens, with everything revolving around our fixed planet, we now find ourselves thrust ever farther from the enormity of the Universe, so that now we are only at the extreme edge of a thing so immense it is almost impossible to conceive.

I was thinking of such things this summer staring up at the Milky Way overhead, and by the way, if you want to do that do hurry up, because each year light pollution makes it harder and harder to see, so that in thirty years the whole planet will be alight by night and day and we can forget the inconvenient truths about how tiny we really are, and get on with the whole business of supplying arms to each other.

I was working on a new version of The Galaxy Song for Professor Brian Cox’s Wonders of Life, and I remembered that some people (including Brian himself) have questioned some of the facts referred to in the original Galaxy Song. When I began to write that song in Provence in 1981 the astronomical distances and speeds mentioned in the lyrics were all considered scientifically accurate: now, of course, we have had thirty years of expanding scientific research and observation and so I have had to alter the words to correspond to our new estimate of the extreme distances in the Galaxy and the ever expanding Universe. Here’s the original lyric.

My comments in italics. Remember he is writing in 2003. The comments from Professor Brian Cox are from this week.

Eric Idle, Monty Python player extraordinaire, wrote the Galaxy Song for the movie The Meaning of Life. I was quite curious to see how it has withstood 20 years of astronomical leaps in our understanding of the universe. My references can be found at http://www.softwarerepair.com/astro/ReferencesforGalaxySong.htm.

Just remember that you’re standing on a planet that’s evolvingWhile still controversial in some areas, evolution seems pretty well established.

Except perhaps in America. Where in some areas evolution is clearly going backwards.

And revolving at nine hundred miles an hour,The speed of the earth’s revolution is once per day (duh) but at the equator the circumference of the earth is 25,000 miles so that makes the speed just over 1,000 miles per hour. However, by the time you get as far north as the UK (Eric Idle’s country) the speed is actually less than 700 miles per hour. The 900 figure might be good enough for our purposes.

And it was written in Provence, further South than the UK.

That’s orbiting at nineteen miles a second, so it’s reckoned,The earth orbits the sun at 29km/second and there is roughly a 3:2 ratio between kilometers and miles so 19 miles per second is pretty close.

A sun that is the source of all our power.This may be a bit of hyperbole. The sun is responsible for all wind and solar power and because our weather depends on the sun we would include hydroelectric power as well. Oil and coal formed as a result of sun-driven processes on earth so that’s okay. But this particular sun did not create uranium so it could be argued that it doesn’t supply all of our power.

I think it was a metaphor not a hyperbole, but I must bow to scientific accuracy. Professor Brian picks up on this too, so I shall have to alter it. This is what he says…

(PBC) “The Sun isn’t the source of all our power. We use heat from the Earth’s core in the form of geothermal energy, and nuclear power comes from Uranium, primarily, which was made in a supernova explosion before the solar system formed. The Earth’s internal heat is part nuclear – Uranium decay and other radioactive isotopes, and part the heat from the gravitational collapse of the solar system’s primordial dust cloud 5 billion years ago – ish. Also, tidal power comes from the Moon’s orbit.”

The sun and you and me and all the stars that we can see
Are moving at a million miles a dayThe sun (and therefore the earth and at least all the stars that you can see with the naked eye) are moving through the galaxy at 225km/sec. This comes out to more than 6 million miles per day.

I shall clearly have to alter this

In an outer spiral arm, at forty thousand miles an hour,We are indeed in an outer spiral arm of the galaxy. If we were moving at a million miles per day that would come out to 40,000 miles an hour. If the number is closer to 6 million miles per day that makes it close to 250,000 MPH.

Hm, this is tricky for the metre. Would you settle for 200,000 miles per hour? Recently I was singing 400,000 miles per hour which is way too much, so I have to change it.

Of the galaxy we call the ‘Milky Way’.
Our galaxy itself contains a hundred billion stars.

While there have been some estimates that are a bit higher than 100 billion stars, this is still a pretty good estimate.

This is Professor Brian’s comment:

(PBC) “Not sure about the latest Milky Way geometry figures, but they are about right. I think the Milky Way stats on its Wikipedia page are accurate. Slightly fewer than 500 billion stars, prob. closer to 300 billion etc.”

So we’ll settle for that then, 300 billion stars.

It’s a hundred thousand light years side to side.Give or take 20,000 light years, this is close to the current estimate.

It bulges in the middle, sixteen thousand light years thick,Estimates vary quite a bit but 10-30 thousand light years is at least one estimate for the middle of the galaxy

So sixteen is right in the middle and can stay right?

But out by us, it’s just three thousand light years wide.And in the outer arms it is anywhere from 1 to 10 thousand light years wide.

I was singing “a thousand” recently but three seems as good as anything.

We’re thirty thousand light years from galactic central point.A very good estimate.

We go round every two hundred million years,Rounding down to the nearest hundred million, this will do nicely.

And our galaxy is only one of millions of billionsMillions of billions would be quite a lot. Some estimates are in excess of 1 trillion galaxies but that’s only thousands of billions. But we aren’t done counting yet.

Now this one Professor Brian does pick up on in this email quote:

(PBC) “I’d be specific that the song is speaking of the observable universe – the sphere around 90 billion light years in diameter. There are around 300 billion large galaxies in the observable universe I think, so a million billion galaxies is too many.”

Fair enough but I think the distinction between the observable universe and non-observable is way too esoteric for the song….

(PBC) “But I think there are also a larger, unknown number of dwarf galaxies. But still less than a million billion!”

Here are some “facts” that I pulled out of David Engelman’s book about the brain: He states there are:

500 million Galaxy groups

10 billion large Galaxies

100 billion dwarf Galaxies

2,000 billion billion suns

The visible Universe is 15 billion light years across and may itself be just a small speck in the total Universe…

But Professor Brian quarrels with this

(PBC) “10 billion is way too low for large galaxies, but this number has changed a lot since the Hubble Deep Field Image was taken. I think the newer number is 300 billion large galaxies, which isn’t far off 110 billion if you count his dwarf galaxies (what’s a factor of 3 between friends). But this is a lot less than a million billion – ten thousand times less in fact. I’ve seen it said there might be a trillion dwarf galaxies, but that’s still only a million million and not a million billion. A million billion is a thousand times more than a million million, which in turn is a thousand times more than a billion :)”

So I have to change this. Can I have millions and billions? Which keeps the original feeling of the line but doesn’t stray from scientific truth.

(PBC) “And it’s definitely 90 million light years side to side … 15 billion in his book comes from the age, but we (of course!!) are speaking of the co-moving distance – i.e. spacetime itself has been stretching for 13.7 billion years, so although it’s only 13.7 billion years old, the distance to the most distant things we can see NOW is greater – around 45 million light years in each direction.”

That’s fine, because it’s the figure we use in the new Galaxy song (qv), as is this reference:

(PBC) “There are certainly well over a billion trillion stars in it, though. The entire Universe, beyond the visible horizon, may be infinite in extent. But we’ll never see it all !”

this amazing and expanding universe.And probably expanding at a faster rate than before.

The universe itself keeps on expanding and expanding
In all of the directions it can whizWe have pretty solid proof of that these days

As fast as it can go, at the speed of light, you know,But matter cannot generally move at the speed of light so the speed of the expansion is somewhat less. On the other hand, there was a time in the early universe where it seems it did expand at a speed greater than the speed of light.

Twelve million miles a minute, and that’s the fastest speed there is.The speed of light is about 186,000 miles per second or just a bit shy of 12 million miles a minute. There are claims for things that can go faster but it is still speculation.

So remember, when you’re feeling very small and insecure,
How amazingly unlikely is your birth,The human genome project has found 30,000 genes. It would take only 33 genes to make every living person unique.

And pray that there’s intelligent life somewhere up in space,
‘Cause there’s bugger all down here on Earth.

Certainly true.

So here is the scientifically correct updated lyric for today. Of course in thirty years you’ll have to change it all again, but I’m afraid you’ll have to do it for me.